Dnia 17.05.2025 o godz. 14:23:35 Alessandro Vesely via mailop pisze:
> 
> After a glance at those sites, I still don't understand what's wrong if a
> certificate could also be used for client authentication.

There is nothing wrong with using a client certificate for authentication
*as such*, but the server cert and client cert functions should be
separated.

Why?

Server cert, like the one obtained from Lets Encrypt, identifies a *server*,
not a particular user. Even if you specify a contact email address in the
cert request, that address is not verified (as far as I remember), and it is
also intended to be a generic administrative address under which the server
operator can be contacted, rather than an address identifying a particular
user.

Client cert, on the other hand, identifies a particular *user*. In our case,
the user's identity would be determined by a particular email address.

I can totally imagine that Lets Encrypt, besides server certs, *could* issue
separate client certs, where you specify your email address in the cert
request, and that address is verified eg. by the usual method - you receive
a confirmation link in email and you have to click on it. Such a cert would
identify a particular email account and could be used to authenticate to the
email server (instead of login and password).

But these functions should not be mixed in the same cert.
-- 
Regards,
   Jaroslaw Rafa
   [email protected]
--
"In a million years, when kids go to school, they're gonna know: once there
was a Hushpuppy, and she lived with her daddy in the Bathtub."
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